37 research outputs found
Laminoplasty versus Laminectomy in the Treatment of Primary Spinal Cord Tumors in Adult Patients: A Systematic Review and Meta-analysis of Observational Studies
The present systematic review and meta-analysis was conducted to compare the safety and efficacy of the two approaches for primary spinal cord tumors (PSCTs) in adult patients (laminoplasty [LP] vs. laminectomy [LE]). LE is one of the most common procedures for PSCTs. Despite advantages of LP, it is not yet widely used in the neurosurgical community worldwide. The efficacy of LP vs. LE remains controversial. Adult patients over 18 years of age with PSCT at the level of the cervical, thoracic, and lumbar spine were included in the study. A literature search was performed in MEDLINE via PubMed, EMBASE, The Cochrane Library, and Google Scholar up to December 2021. Operation time, hospital stay, complications, and incidence of postoperative spinal deformity (kyphosis or scoliosis were extracted. A total of seven retrospective observational studies with 540 patients were included. There were no significant differences between LP and LE group in operation time (p=0.25) and complications (p=0.48). The LE group showed larger postoperative spinal deformity rate than the LP group (odds ratio, 0.47; 95% confidence interval [CI], 0.27−0.84; p=0.01). The LP group had a shorter hospital stay (standardized mean differences, −0.68; 95% CI, −1.03 to −0.34; p=0.0001) than the LE group. Both LP and LE have comparable operative times and total complications in the treatment of PSCT. LP was superior to LE in hospital stay and postoperative spinal deformity rate. However, these findings are limited by the very low quality of the available evidence. Randomized controlled trials are needed for further comparison
The choice of the optimal approximation in the kinetic description of the vacuum creation of electron-positron plasma in strong laser fields
The paper justifies 2-similarity of kinetic equation solutions to describe vacuum emergence of electronpositron plasma under the effect of strong “laser” fields, where () is the intensity of the strong time-dependent “laser” field. The boundaries of existence of this similarity were studied
Peering into the tilted heart of Cyg X-1 with high-precision optical polarimetry
We present the high-precision optical polarimetric observations of black hole
X-ray binary Cyg X-1, spanning several cycles of its 5.6 day orbital period.
Week-long observations on two telescopes located in opposite hemispheres
allowed us to track the evolution of the polarization within one orbital cycle
with the highest temporal resolution to date. Using the field stars, we
determine the interstellar polarization in the source direction and
subsequently its intrinsic polarization. The optical polarization angle is
aligned with that in the X-rays as recently obtained with the Imaging X-ray
Polarimetry Explorer. Furthermore, it is consistent, within the uncertainties,
with the position angle of the radio ejections. We show that the intrinsic PD
is variable with the orbital period with the amplitude of 0.2% and
discuss various sites of its production. Assuming the polarization arises from
a single Thomson scattering of the primary star radiation by the matter that
follows the black hole in its orbital motion, we constrain the inclination of
the binary orbit and its eccentricity . The asymmetric
shape of the orbital profiles of Stokes parameters implies also the asymmetry
of the scattering matter distribution about the orbital plane, which may arise
from the tilted accretion disk. We compare our data to the polarimetric
observations made over 1975-1987 and find good, within , agreement
between the intrinsic polarization angles. On the other hand, the PD decreased
by 0.4% over half a century, suggesting the presence of secular changes in the
geometry of accreting matter.Comment: 12 pages, 18 figure
Orbital variability of the optical linear polarization of the -ray binary LS I +61 303 and new constraints on the orbital parameters
We studied the variability of the linear polarization and brightness of the
-ray binary LS I +61 303. High-precision BVR photopolarimetric
observations were carried out with the Dipol-2 polarimeter on the 2.2 m
remotely controlled UH88 telescope at Mauna Kea Observatory and the 60 cm
Tohoku telescope at Haleakala Observatory (Hawaii) over 140 nights in
2016--2019. We determined the position angle of the intrinsic polarization
, which can either be associated with the projection of
the Be star's decretion disk axis on the plane of sky, or can differ from it by
. Using the Lomb-Scargle method, we performed timing analyses and
period searches of our polarimetric and photometric data. We found
statistically significant periodic variability of the normalized Stokes
parameters and in all passbands. The most significant period of
variability, d, is equal to one half of the
orbital period d. Using a model of Thomson scattering
by a cloud that orbits the Be star, we obtained constraints on the orbital
parameters, including a small eccentricity and periastron phase of
, which coincides with the peaks in the radio, X-ray,
and TeV emission. These constraints are independent of the assumption about the
orientation of the decretion disk plane on the sky. We also extensively discuss
the apparent inconsistency with the previous measurements of the orbital
parameters from radial velocities. By folding the photometry data acquired
during a three-year time span with the orbital period, we found a linear phase
shift of the moments of the brightness maximum, confirming the possible
existence of superorbital variability.Comment: 15 pages, 16 figures, accepted for publication in A&
Передмова
It is a brief description of the Volume II of the proceedings of ICTERI 2021.Дається короткий опис тому ІІ збірника матеріалів конференції ICTERI 2021
Optical polarization signatures of black hole X-ray binaries
Polarimetry provides an avenue for probing the geometry and physical mechanisms producing optical radiation in many astrophysical objects, including stellar binary systems. We present the results of multiwavelength (BVR) polarimetric studies of a sample of historical black hole X-ray binaries, observed during their outbursts or in the quiescent (or near-quiescent) state. We surveyed both long- and short-period systems, located at different Galactic latitudes. We performed careful analysis of the interstellar polarization in the direction on the sources to reliably estimate the intrinsic source polarization. Intrinsic polarization was found to be small (5 per cent) intrinsic quiescent-state polarization with a blue spectrum. The absence of intrinsic polarization at the optical wavelengths puts constraints on the potential contribution of non-stellar (jet, hot flow, accretion disc) components to the total spectra of black hole X-ray binaries